1. Field of the Invention
This invention relates to the preparation of cyclic ureas, and, more particularly, is concerned with the preparation of bis cyclic ureas which can act as masked diisocyanates, the diisocyanates produced thereby, and the stable one-component polyurethane forming systems containing said bis cyclic ureas.
2. Description of the Prior Art
One-can, or the commonly named one-component, polyurethane forming systems are well known, particularly, in the coating art; see for example, Saunders & Frisch, Polyurethanes: Chemistry and Technology, Parts I (pp. 8 and 118-121) and II, (pp. 453-454), 1963 and 1964 respectively, Interscience Publishers, John Wiley and Sons, New York, N.Y., and further references cited therein. The one-component systems call for the use of a "blocked" or "disguised" isocyanate with a polyol. Upon heating the one-component system, the isocyanate groups are released to react with the polyol to form the polyurethane. Unless, and until, the systems are heated they remain shelf stable and avoid the need to store and mix a number of separate components.
However, the blocked isocyanates suffer from the severe disadvantage that when the blocking agent is released during the curing phase, it is liberated into the resin where it may remain and have a deleterious effect, or, alternatively, be vaporized off where it must either be collected or released to the atmosphere. Since the commonest blocking agent is phenol this gives rise to both safety and environmental problems, not to mention the economic ones.
We have now found a novel class of bis cyclic ureas which are particularly useful in stable one-component polyurethane systems where they function as masked isocyanates. When the system is heated the bis ureas dissociate to form only the diisocyanate thereby eliminating the prior art problem of a released blocking agent.
Furthermore, the compounds prepared from the bis cyclic ureas are, themselves, a novel class of amide containing diisocyanates which are useful monomers in applications other than one-component polyurethane systems and are very simply prepared from said ureas.